In a half-duplex communication system operable in temporally separated transmit and receive modes of operation, a transmit filter is generally inserted between a power amplifier and a communication medium such as an alternating current (“ac”) power line to provide an appropriate level of suppression of out-of-band frequency components. Correspondingly, a receive filter is generally inserted between the communication medium and a receiver input port of the half-duplex communication system to manage out-of-band noise and interference at the input of the receiver. The result of this configuration is that both filters are coupled in parallel to the communication medium. Design trade-offs to meet separate specifications are a result of this coupling, which impacts the physical size of the filtering functions and cost of the end product. Techniques to mitigate design constraints for the parallel filtering functions would provide welcome design relief.
In a typical implementation of a bandpass communication system, a transmitter driver and a transmitter power amplifier operate in the linear mode. A transmitter output of a transceiver is a bandpass modulated signal confined by communication requirements to a limited range of frequencies. Various functional blocks in a transmitter and a receiver (or a transceiver) are formed as different pieces of hardware, often being implemented in separate integrated circuits in combination with a variety of discrete components. The overall design also often includes two separate voltage supply rails, one to power low-voltage circuitry of the communication system and one to power high-voltage circuitry therein.
Transceiver signal processing and control functionalities of the communication system are frequently absorbed into a microprocessor control unit/central processing unit (“MCU/CPU”). To improve power efficiency, a driver and power amplifier are formed of a switching type and a single low-voltage supply is employed to power the same. The use of a switch-mode driver and power amplifier requires a two-level transceiver transmitter output signal within which the desired bandpass signal has been encoded.
There are a variety of different methods that can be utilized to encode the information-bearing bandpass signal into a two-level signal suitable for transmission via a switch-mode power amplifier. One such encoding method employs a discrete-time delta-sigma modulator (“DTDSM”) to convert a modulated bandpass signal into a discrete-time two-level (i.e., binary) signal.
In operation, the transmitter takes information data bits (or symbols) to be transmitted as an input, generates the desired passband signal using the modulator, then encodes the passband signal into a two-level discrete signal with the DTDSM. Finally, a two-level signal suitable for input to a switch-mode power amplifier is produced by way of a zero-order hold circuit. In this way, the modulator (e.g., DTDSM) and the zero-order hold circuit are active when the passband signal is being transmitted and necessarily consume extensive computational resources (and electrical energy).
To achieve high signal-to-noise ratio (“SNR”) levels and a wide DTDSM passband, the DTDSM executes at a high rate, which increases the design complexity and cost of the DTDSM. Descriptions herein provide approaches that reduce the computational resources by the modulator thereby providing economy in the design of such communication systems.
Corresponding numerals and symbols in the different FIGUREs generally refer to corresponding parts unless otherwise indicated. The FIGUREs are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.